For years there have been improvements in the technology of screw making. Heretofore, threads were cut by lathe directly. Sequential screw cutting lathes were used and then different dies were applied. However, each die can be used for making simple screws conforming to one specification. Ways of using the dies are:
(1) Cylindrical Die Thread Rolling, which is sub-divided into a two-die type and a three-die type. Its principle is the rolling of working pieces in two or three dies to make threads and form screws.
(2) Radial Rolling, by which a working piece is placed between two dies and their mutual movement threads the working piece and forms a screw.
In addition, penetration rolling and other methods have been used. In these methods, the die itself may involve the space for rolling and accuracy of threading. More complicated feeding equipment is thus required. Therefore, in the application of any of these above methods, the speed is low and mass production becomes impossible.